1. Field of the Invention
The present invention relates to alight bulb type fluorescent lamp lighting apparatus for lighting up a fluorescent light emitting tube using a high frequency inverter type electronic lighting circuit.
2. Description of the Related Art
In recent years, as energy savings have become more and more important, an increasing number of fluorescent lamp light apparatuses have adopted a high frequency inverter type electronic lighting circuit, instead of a copper-iron stabilizer as conventionally used. Specifically for a light bulb type fluorescent lamp built in the lighting apparatus as an energy-saving light source replacing a light bulb, the use of this type of electronic lighting circuits is becoming more common in order to realize a lamp having a higher lamp efficiency or light emission efficiency.
In order to improve the lamp efficiency of the electronic lighting circuit for a light bulb type fluorescent lamp, there has been an attempt to improve the circuit conversion efficiency of the electronic lighting circuit. As a result, the circuit conversion efficiency which was about 80% has been increased to a maximum of about 92%. This has been realized by introducing a series inverter circuit system in an electronic light circuit or by using a MOS field emission power transistor as an electronic component. The value of about 92% is almost the maximum possible value for circuit conversion efficiency. In order to further improve the lamp efficiency, a different new technique, for example, a technique for reducing a power loss caused by heat generation in an electrode filament coil in the fluorescent light emitting tube is demanded.
FIG. 4 is a diagram illustrating a basic structure of a conventional high frequency inverter type electronic lighting circuit 119 (hereinafter, referred to simply as the xe2x80x9celectronic lighting circuit 119xe2x80x9d). The electronic lighting circuit 119 includes an inverter circuit section 125 which is driven by a commercial power supply 113. The inverter circuit section 125 lights up a fluorescent light emitting tube 120.
The fluorescent light emitting tube 120 includes a pair of electrode filament coils 121 and 122. The electrode filament coil 121 includes terminals 121a and 121b, and the electrode filament coil 122 includes terminals 122a and 122b. The terminals 121a and 122a are closer than the terminals 121b and 122b to the power supply 113 for applying an electric current to the fluorescent light emitting tube 120.
The terminal 122a of the electrode filament coil 122 is directly connected to the inverter circuit section 125. The terminal 121a of the electrode filament coil 121 is connected to the inverter circuit section 125 via an inductor 124 provided for electric current control. The inductor 124 is connected in series to the terminal 121a. The terminals 121b and 122b of the electrode filament coils 121 and 122 are connected to each other via a capacitor 123. The capacitor 123 and the inductor 124 are included in a resonating circuit. In FIG. 4, an inductance of the inductor 124 is represented by xe2x80x9cLxe2x80x9d, and a capacitance of the capacitor 123 is represented by xe2x80x9cCsxe2x80x9d.
The conventional electronic lighting circuit 119 performs an operation for starting and thus placing a fluorescent lamp into a constant lighting state, using a hot cathode starting system. This will be described below.
Before starting the lamp, the inverter circuit section 125 causes an electric current to flow to the electrode filament coils 121 and 122 of the fluorescent light emitting tube 120 through the capacitor 123 in order to pre-heat the electrode filament coils 121 and 122 and thus cause the electrode filament coils 121 and 122 to emit a sufficient amount of thermoelectrons. The capacitor 123 is connected parallel to the fluorescent light emitting tube 120.
When the pre-heating electric current is supplied to the electrode filament coils 121 and 122, a starting voltage is applied between the electrode filament coils 121 and 122 within about 1 second, and thus the fluorescent light emitting tube 120 is started. The starting voltage corresponds to a resonating voltage of the resonating circuit including the capacitor 123 and the inductor 124.
The fluorescent light emitting tube 120, after being started, goes into a constant lighting state. In this state, the electric current still flows to the electrode filament coils 121 and 122 via the capacitor 123, and thus heat is generated in the electrode filament coils 121 and 122.
As described above, the conventional electronic lighting circuit 119 realizes the constant lighting state of the fluorescent light emitting tube 120 after pre-heating the electrode filament coils 121 and 122 and then starting the fluorescent light emitting tube 120. After the fluorescent light emitting tube 120 goes into the constant lighting state, the electric current for heating the electrode filament coils 121 and 122 is basically unnecessary. However, since an electric current is required in order to pre-heat the electrode filament coils 121 and 122 by the conventional method, the electric current inevitably flows even after the fluorescent light emitting tube 120 goes into the constant lighting state and thus generates heat in the electrode filament coils 121 and 122. This heat generation causes a power loss.
In a currently-used light bulb type fluorescent lamp (for example, a 14 W or 25 W light bulb) which has a luminous flux corresponding to that of a general 60 W or 100 W light bulb, the power loss caused by the heat generation is 0.4 W to 0.5 W per electrode filament coil. In the fluorescent light emitting tube 120, the power loss caused by the heat generation is 0.8 W to 1.0 W per electrode filament coil. These values are not negligible.
FIGS. 5A through 5C show known electronic light circuits used for reducing such a power loss caused by the heat generation in an electrode filament coil during a constant light state of the fluorescent light emitting tube 120. Like elements as those in FIG. 4 bear identical reference numerals.
An electronic light circuit 119a shown in FIG. 5A adopts a so-called cold cathode starting system. The electrode filament coils 121 and 122 of the fluorescent light emitting tube 120 are respectively shortcircuited by leads 126 and 127. The leads 126 and 127 are respectively connected parallel to the electrode filament coils 121 and 122. The fluorescent light emitting tube 120 is started in a cold cathode state with no thermoelectrons being emitted. Due to such a structure, the power loss caused by the heat generation in the electrode filament coils 121 and 122 is reduced.
An electronic lighting circuit 119b shown in FIG. 5B is disclosed in Japanese Laid-Open Publication No. 10-199686. Diodes 128 and 129 are respectively connected parallel to the electrode filament coils 121 and 122 of the fluorescent light emitting tube 120. Due to such a structure, the amount of the electric current flowing to each of the electrode filament coils 121 and 122 is reduced to half. Thus, the power loss caused by the heat generation is also reduced to about half.
An electronic lighting circuit 119c shown in FIG. 5C is disclosed in Japanese Laid-Open Publication No. 5-13186. Capacitors 131 and 132 are respectively connected parallel to the electrode filament coils 121 and 122 of the fluorescent light emitting tube 120. The capacitor 131 branches the electric current into the capacitor 131 and the electrode filament coil 121, and the capacitor 132 branches the electric current into the capacitor 132 and the electrode filament coil 122. Due to such a structure also, the amount of the electric current flowing to each of the electrode filament coils 121 and 122 is reduced. Thus, the power loss caused by the heat generation is also reduced.
Fluorescent lamps are now expected to be used in houses which is one important field of use of light bulbs, in addition to department stores, restaurants, hotels and other business settings in which the fluorescent lamps are mainly used. Generally in fluorescent lamps, an electron radiating substance filling the electrode filament coils at the time of starting the lamp easily scatters. Accordingly, it is known that as the number of times the fluorescent lamp is lit on or off is increased, the life of the lamp is shortened. This is also true with light bulb type fluorescent lamps. Lamps which are used in houses are inevitably lit on or off a greater number of times than lamps used in business settings. It is required that the number of times the lamp can be lit on and off until the life of the lamp ends (hereinafter, the number of times the lamp can be lit on and off until the life of the lamp ends will be referred to as the xe2x80x9clamp life lighting on/off characteristicxe2x80x9d) be increased.
The lamp life lighting on/off characteristic is conventionally about 5000 times. Now, the lamp life lighting on/off characteristic is required to be increased to be 4 times larger, i.e., at least 20000 times. According to an experiment performed by the present inventors, the average life of the conventional lamp was 6000 hours. This corresponds to an average life obtained in a test by which the lamp is kept on for 2.5 hours and then kept off for 0.5 hours.
In order to respond to this demand, Japanese Laid-Open Publication No. 62-126596 discloses an electronic lighting circuit 140 shown in FIG. 6. A temperature positive characteristic resistance element (positive character thermistor or PCT) 133 is connected parallel to the capacitor 123 so as to be opposite to the commercial power supply 113 with respect to the fluorescent light emitting tube 120. Due to such a structure, a large amount of pre-heating electric current flows to the electrode filament coils 121 and 122 via the temperature positive characteristic resistance element 133 before the fluorescent light emitting tube 120 is started. Thus, the lamp life lighting on/off characteristic is improved.
The present inventors performed studies on a fluorescent lamp using an electronic lighting circuit, specifically a light bulb type fluorescent lamp having a built-in electronic lighting circuit, in order to realize both reduction in a power loss caused by the heat generation in an electrode filament coil in the constant lighting state of the lamp and an increase in the lamp life lighting on/off characteristic. As a result, the present inventors found that the electronic lighting circuits shown in FIGS. 5A through 5C have an undesirable possibility that the lamp life lighting on/off characteristic is not increased.
In the cold cathode starting system shown in FIG. 5A with no emission of thermoelectrons, the power loss caused by the heat generation in the coils can sufficiently be reduced. However, the voltage for starting the fluorescent light emitting tube 120 needs to be applied for an extended period of time. Thus, the glow discharge time period, immediately after the fluorescent light emitting tube 120 is started, is also relatively long. As a result, the electron radiating substance filling the electrode filament coils 121 and 122 scatters more violently than in a circuit adopting the usual hot cathode starting system, and therefore there is an undesirable possibility of reducing the lamp life lighting on/off characteristic.
In the structure shown in FIG. 5B including the diodes 128 and 129 connected parallel to the electrode filament coils 121 and 122 respectively and the structure shown in FIG. 5C including the capacitors 131 and 132 connected parallel to the electrode filament coils 121 and 122 respectively, the effect of reducing the power loss is relatively small. Moreover, a sufficient number of thermoelectrons are not emitted since a sufficient amount of pre-heating electric current does not flow to the electrode filament coils 121 and 122 before the fluorescent light emitting tube 120 is started. As a result, a larger amount of electron radiating substance scatters, which involves an undesirable possibility of not increasing the lamp life lighting on/off characteristic.
In the structure shown in FIG. 6, a sufficient amount of pre-heating electric current can flow to the electrode filament coils 121 and 122 before an electric current for starting the fluorescent light emitting tube 120 flows, which significantly increases the lamp life lighting on/off characteristic. However, the power loss caused by the heat generation in the electrode filament coils 121 and 122 during the constant light state of the fluorescent light emitting tube 120 is not reduced. The power loss is almost the same as that in the conventional electronic lighting circuit 119 shown in FIG. 4.
A light bulb type fluorescent lamp lighting apparatus according to the present invention includes a fluorescent light emitting tube; and an electronic lighting circuit for applying an electric current to the fluorescent light emitting tube. The electronic lighting circuit includes a pair of electrode filaments provided in the fluorescent light emitting tube, a capacitor connected parallel to the fluorescent light emitting tube, an inductor connected in series to one of the pair of electrode filaments, a temperature positive characteristic resistance element connected parallel to the capacitor, and at least one temperature negative characteristic resistance element connected parallel to at least one of the pair of electrode filaments.
In one embodiment of the invention, the number of the at least one temperature negative characteristic resistance element is two, and the two temperature negative characteristic resistance elements are respectively connected parallel to the pair of electrode filaments.
In one embodiment of the invention, the at least one temperature negative characteristic resistance element is connected to either one of the pair of electrode filaments.
In one embodiment of the invention, the electronic lighting circuit further includes an inverter circuit section for supplying an electric current for lighting up the fluorescent emitting tube.
A light bulb type fluorescent lamp lighting apparatus according to the present invention includes a fluorescent light emitting tube; and an electronic lighting circuit for applying an electric current to the fluorescent light emitting tube. The electronic lighting circuit includes a pair of electrode filaments provided in the fluorescent light emitting tube, a capacitor connected parallel to the fluorescent light emitting tube, an inductor connected in series to one of the pair of electrode filaments, and at least one temperature negative characteristic resistance element connected parallel to at least one of the pair of electrode filaments. The at least one temperature negative characteristic resistance element has a resistance impedance, and the fluorescent light emitting tube is started based on a change in the resistance impedance of the at least one temperature negative characteristic resistance element.
In one embodiment of the invention, the number of the at least one temperature negative characteristic resistance element is two, and the two temperature negative characteristic resistance elements are respectively connected parallel to the pair of electrode filaments.
In one embodiment of the invention, the at least one temperature negative characteristic resistance element is connected to either one of the pair of electrode filaments.
In one embodiment of the invention, the electronic lighting circuit further includes a temperature positive characteristic resistance element connected parallel to the capacitor.
In one embodiment of the invention, the electronic lighting circuit further includes an inverter circuit section for supplying an electric current for lighting up the fluorescent emitting tube.
Thus, the invention described herein makes possible the advantages of providing a fluorescent lamp lighting apparatus for reducing a power loss caused by heat generation in an electrode filament coil during a constant lighting state of a fluorescent light emitting tube and also increasing a lamp life lighting on/off characteristic.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.